module SessionsHelper
    def log_in(user)
     session[:user_id] = user.id
    end


    def current_user
        if session[:user_id]
            @current_user ||= User.find_by(id: session[:user_id])
        end
    end
    
    def  logged_in?
           !current_user.nil?
    end
    
     #退出当前用户
  def log_out
      session.delete(:user_id)
      @current_user = nil
  end
end
